Northern Virginia motorists were promised a "Christmas present" last week when the General Assembly passed a bill to delay a controversial auto exhaust testing program for another year.

But yesterday some officials were saying the program, which already has tested 11,000 cars, is likely to continue.

Governor John N. Dalton had not decided by then whether to sign or veto the bill to delay the tests, although that decision is expected today. The state's Division of Motor Vehicles still is refusing to issue registration renewals without evidence that the test has been passed.

"Until the governor takes some action one way or another, we have to act as if the law is still in effect," said an official with Virginia's DMV, which recently sent test notices to more than 30,000 car owners in Northern Virginia whose registrations expire in January.

Dalton aides say the governor would like to sign the bill and save the 500,000 motorists in Northern Virginia the $3.50 fee for the test and as much as $75 in repairs they could be forced to spend to pass it. But Dalton is afraid Virginia could lose as much as $350 million in federal highway funds if it refuses to comply with an Environmental Protection Agency order mandating that the tests begin by Jan. 1.

With Virginia's Highway Department already suffering severe budget problems, Dalton is reportedly playing a cautious hand with the EPA.

"This octopus has a heck of a lot of tentacles that probably haven't been thought about as much as they should," said Dalton spokesman Charles Davis, who said the governor has met with state officials for the last two days to discuss strategy. "We don't want to risk unnecessarily fooling around with hundreds of millions of dollars."

"He honestly has not made a decision," said Davis. "Meanwhile it's like the swan on the lake: It's very calm on the surface but pumping like hell underwater."

The emissions tests are mandated by the Clean Air Act of 1970. Washington is one of 37 metropolitan areas across the country where the EPA determined there is excessive carbon monoxide or smog in the atmosphere. Though Northern Virginia, except Loudoun County, was told to begin testing in 1982, Maryland and the District of Columbia were given one more year to start the program.

"Virginia shouldn't be in the position of having to foot this bill alone," said Del. David Brickley (D-Prince William) last week as he stood on the floor of the General Assembly in Richmond and persuaded his colleagues to delay the program that they had grudgingly approved last spring. "If we ever needed to have a Christmas present or a Hanukah present, this is the time."

EPA officials this week explained that Virginia was not given the same one year extension as Maryland and the District because its inspection program, performed at 350 private service stations, is already "decentralized." In Maryland, where auto inspections are needed only when cars are bought or sold, new inspection stations would have to be built to accommodate annual testing.

Virginia officials complain that the District, which already conducts annual inspections, has no better excuse for a delay. Besides, they argue, the three jurisdictions are so close together that cleaning exhausts in only one area will improve the overall air quality only moderately.

"I know ozone does cross state lines," said an official at the EPA's Office of Mobile Source Air Pollution Control in Ann Arbor, Mich., who asked to remain unnamed. "But the EPA wasn't really in a position to differentiate between states. It is both reasonable and unreasonable that they start at different times."

Yesterday, cars were still lining up for the emissions testing.

About 100 service stations in Arlington, Fairfax and Prince William counties, the cities of Alexandria, Fairfax and Falls Church and the towns of Manassas and Manassas Park are equipped to test auto exhausts. Owners of those stations have purchased infrared analyzers that cost from $2,500 to $9,000. To be certified to operate the equipment, service station employes were required to attend a six-day course at area community colleges.